Question: What theory did Grigori Perelman prove?
Paraphrase: What was Grigori Perelman's proven theory?
SPARQL (Wikidata):  select distinct ?sbj where { ?sbj wdt:P1318 wd:Q117346 . ?sbj wdt:P31 wd:Q65943 } 
Answer: Poincaré conjecture, soul